Start Firefox in Safe Mode to Troubleshoot the issue and to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

I can't get a consistent result. Sometimes it helps, sometimes it doesn't. As if Firefox either gets in its own way or not, independent of addon disabling.

I have ad block and flash block and adobe dlm.

One clue is that, if you run task manager "performance" graph, sometimes Firefox preempts the time task manager gets to update and shift the graph, and the updating stops dead. It resumes updating if you put task manager in the foreground (so Firefox is no longer the foreground window).

Additional clue : pages load much faster if you minimize Firefox. Perhaps it stumbles over itself trying to keep the visible page current repeatedly, which it does not do if the page isn't on the screen.

When is the last time you scanned the computer for mal-ware? I do not mean anti-virus.

Sometimes a problem with Firefox may be a result of malware installed on your computer, that you may not be aware of.

You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• Anti-Rootkit Utility - TDSSKiller
• AdwCleaner (for more info, see this alternate AdwCleaner download page)
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Did this fix your problems? Please report back to us!

It can't be. Reinstalling Firefox 26.0 works fine. 27.0 was the first that ate up cpu cycles.

Is there a Firefox cpu profile tool that can give an account of where the cpu is spending its time?

It seems like that would quickly answer all these kinds of problems.

Update your Shockwave Flash v14. http://get.adobe.com/shockwave/ The link for Flash Player is: http://get.adobe.com/flashplayer/

New Flash doesn't change anything. (just tried)

Here's what I think are the two key clues :

1. Task manager updates cease when Firefox is in its cpu-hanging state. So whatever it's doing is crowding out even the high priority task manager.

2. When Firefox is cpu-crowding, if you minimize the Firefox window, it appears to clear up and operate normally. So the work-around is

2a. Start loading all the tabs you'll need, and

2b. Get Firefox off the screen. Watch the task manager listing for Firefox to see when it finishes, and then return it to the screen.

I think that "restores" Firefox to 26.0 speeds.

So : what, in XP Home, single core cpu, is Firefox 27.0 and following ones doing that goes cpu crazy when Firefox is on the screen?

Don't know if this is what you want, but;

https://addons.mozilla.org/en-US/firefox/search/?q=cpu Add-on Search Results for "cpu"

It could be the work of one of your add-ons, or even add / mal-ware. Look thru your add-ons list and make sure you know what each one is and what it does. Also, check the programs that are on your computer

Windows: Start > Control Panel > Uninstall Programs. Mac: Open the "Applications" folder Linux:

• Ubuntu Unity {web link}
• Xfce: Applications Menu category sections
• options depends on the package manager and the desktop environment

Go thru the list. If you find something that you don't know what it is, use a web search.

Troubleshoot Firefox Issues Caused By Malware {web link}

The malware theory, and the add-on theory, has to account for its working fine in Firefox 26.0 and not Firefox 27-31.

What I wanted is a traditional cpu location profile, preferably with addresses referred back to the Firefox source.

The mechanism is using (say) a clock interrupt and noting the location counter, and forming a count of occurences in each segment of Firefox code.

Wherever it's hanging up the CPU will produce an enormous count there, and probably shows where whatever race condition has been introduced.

Fixed! From hints found on this site

Enter about:config in the address bar

click i'll be careful

two entries need changing

gfx.canvas.azure.backends - remove "cairo" gfx.content.azure.backends - remove "cairo"

restart and all is well. I think. So far.

UPDATE: It's better but still seriously hanging. For instance it still displaces the task manager update cycle unless Firefox is minimized off the screen. Maybe there's another cairo somewhere.

Another clue : sometimes on a new page the CPU usage and memory usage square plots from the task manager prints through and is preserved as a snapshot on the Firefox completed page.

It's somehow competing with task manager and screwing things up.

Is it possible that the tabs' circling green loading indicator is the whole problem?

If I conceal these with another window it appears to speed up a lot.

Say that keeping the circle going takes a lot of cpu power at a high task priority (high enough to displace the "above normal" task manager).

Is there a way to turn this off?

UPDATE : this appears to solve the problem. Turn off the loading tab green circles somehow. I don't know how to do it automatically though. Either minimize the page or cover the top of the browser with a wide thin notepad until it finishes loading.

Didn't the green loading circles start with v 27.0? That's when the problem started.